Method of creating a spring Brassica napus

ABSTRACT

Crossing a winter  B. napus  line with a rapid-cycle  B. rapa  line has been discovered to provide an unexpectedly simple and efficient way to create a modified  B. napus  with a spring flowering habit. In one implementation, such a modified  B. napus  or its progeny is crossed with a second winter  B. napus  line to produce a plant having a winter flowering habit. This allows one to significantly shorten the development cycle for winter-flowering  B. napus  lines by conducting part of the breeding program with spring-flowering time cycles, then migrating the resultant germplasm back into a winter-flowering line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a national phase entry of International Application No.PCT/US2010/036911, filed 1 Jun. 2010 and entitled METHOD OF CREATING ASPRING BRASSICA NAPUS, which claims the benefit of U.S. ProvisionalApplication No. 61/217,513, filed 31 May 2009 and entitled METHOD OFCREATING A SPRING BRASSICA NAPUS.

TECHNICAL FIELD

The present disclosure relates generally to breeding of Brassica napus.The invention has particular utility in creating spring B. napus linesfrom winter B. napus lines.

BACKGROUND

Brassica napus is grown commercially to produce edible oil that is lowin saturated fat. In Europe, B. napus is commonly referred to asrapeseed or rape. Most B. napus commercially produced in North Americais canola, which by definition must produce seed that yields oil havingless than 2% erucic acid and meal that contains no more than 30micromoles of the following glucosinolates per gram of air-dry, oil-freesolid: 3-butenyl glucosinolate, 4-pentenyl glucosinolate, 2-hydroxy-3butenyl glucosinolate, and 2-hydroxy-4-pentenyl glucosinolate. As usedherein, a “non-canola” B. napus line is one which does not meet thisdefinition, e.g., because the seeds produce oil with too much erucicacid or have too high a glucosinolate level.

Most B. napus lines are typically classified as either spring lines orwinter lines. Winter lines are commonly planted in the autumn and flowerin the spring after a period of vernalization over the winter. Springlines do not require vernalization to flower and are commonly plantedand harvested in the same growing season. Winter lines are common inEurope, but most winter lines fare poorly in the colder winters ofCanada and the northern United States. As a consequence, most B. napusgrown commercially in North America are spring lines.

Although open-pollinated B. napus lines remain quite common, commercialproduction of spring B. napus increasingly employs hybrid lines. Hybridlines tend to have higher yields due to heterosis or “hybrid vigor”.This heterosis is more pronounced the more distant the geneticrelationship between the parent B. napus lines.

For this reason, several researchers have suggested crossing winter andspring B. napus lines to produce higher-yielding hybrids. For example,U.S. Pat. No. 6,069,302 (“Osborn”, the entirety of which is incorporatedherein by reference) proposes crossing a spring B. napus line with a B.napus line that is itself derived from at least one winter line.

DETAILED DESCRIPTION

Definitions

As used herein, a “winter B. napus” is a B. napus that has a winterflowering habit, i.e., that does not germinate, initiate vegetativegrowth, undergo gametogenesis and flower in less than 77 days whensubjected to the following conditions, which are referred to below as“standardized growing conditions” or simply “SGCs”: the seeds areplanted in 4-inch plastic pots in a general growth medium (e.g., PremierPro-Mix BX potting soil from Permier Horticulture of Quebec, Canada) inan environmentally controlled growth cabinet (e.g., Conviron ATC60 fromControlled Environments Limited of Winnipeg, Manitoba) with a 16 hourphotoperiod, a day time temperature of 20 degrees Celsius and night timetemperature of 17 degrees Celsius, watered daily as needed and a20:20:20 (NPK) liquid fertilizer added three times weekly.

As used herein, a “spring B. napus” is a B. napus that has a springflowering habit, i.e., that will germinate, initiate vegetative growth,undergo gametogenesis and flower in no more than 55 days when subjectedto the aforementioned standardized growing conditions.

A “rapid-cycle Brassica rapa”, as that term is used herein, is a B. rapathat has a rapid-cycle flowering habit, i.e., that will germinate,initiate vegetative growth, undergo gametogenesis and flower in no morethan 20 days when subjected to the standardized growing conditionsdetailed above. As it flowers in less than 55 days, a “rapid-cycleBrassica rapa” may also be said to have a spring flowering habit.

Overview

Specific details of several embodiments of the disclosure are describedbelow. One aspect of the present disclosure is directed toward a methodfor producing a modified Brassica napus. In accordance with this method,a first winter B. napus line is crossed with a rapid-cycle B. rapa linein a first cross, thereby producing an F1 modified B. napus plant thathas a spring flowering habit. The rapid-cycle B. rapa line has a meanflowering time under standardized growing conditions of no greater than20 days. After the first cross, seed from the F1 modified B. napus plant(or progeny thereof) is crossed with a second winter B. napus line in asecond cross to produce a plant, which may be referred to as a firstbackcross (BC1) plant, that has a spring flowering habit.

Another embodiment of the invention provides a method for producing amodified Brassica napus having a winter flowering habit. In this method,a first winter B. napus line is crossed with a rapid-cycle B. rapa linein a first cross, thereby producing an F1 modified B. napus plant thathas a spring flowering habit. The rapid-cycle B. rapa line has a meanflowering time under standardized growing conditions of no greater than20 days. After the first cross, the F1 modified B. napus plant (orprogeny thereof) is crossed with a second winter B. napus line in asecond cross to produce a first backcross population. From the firstbackcross population, at least one first backcross (BC1) plant that hasa spring flowering habit is selected. Thereafter, the BC1 plant orprogeny thereof is crossed with a third winter B. napus line in a thirdcross to produce a second backcross plant population. From the secondbackcross plant population, at least one second backcross (BC-W) plantthat has a winter flowering habit is selected.

Producing F1 Spring B. napus

Aspects of the invention are directed to the production of a springmodified B. napus line by crossing a winter B. napus line with arapid-cycle Brassica rapa line. In a preferred embodiment, the winter B.napus line used in the cross will not germinate, initiate vegetativegrowth, undergo gametogenesis and flower at all unless subjected tovernalization. Although this is no guarantee, a line that is less proneto flower without vernalization may have a more distant geneticrelationship to most common spring B. napus lines (defined below). As aconsequence, one might predict that crossing such a winter B. napus linewith a common spring B. napus line would yield a hybrid with greaterheterosis than would a winter line that flowers more readily.

Several restriction fragmentation length polymorphisms (RFLPs) have beenlinked to specific vernalization-responsive flowering time loci. See,e.g., Ferreira, M. E., et al., “Mapping Loci Controlling VernalizationRequirement and Flowering Time in Brassica napus,” Theor. Appl. Genet.98:727-732 (1995); see also Osborn, T. C. et al, “Comparison ofFlowering Time Genes in Brassica rapa, B. napus, and Arabadopsisthaliana,” Genetics 146:1123-1129 (1997). These include vfn1, which wasmapped as a quantitative trait locus (QTL) of Linkage Group (LG) 9;vfn2, which was mapped as a QTL of LG12; and vfn3, which was mapped toLG16. Osborn identifies suitable RFLP loci to distinguish winter andspring vfn1 and vfn2 alleles and provides sequences that may be used forPCR probes to screen for winter vfn1 and vfn2 alleles.

Winter B. napus lines suitable for use in the present method may (butneed not) have winter alleles for one, two, or three of the vfn1, vfn2,and vfn3 loci. In one useful implementation, the winter B. napus lineused in the present method has a homozygotic winter vfn1 allele.

A wide variety of suitable winter B. napus lines are known and availableto breeders from a variety of sources. A non-limiting, partial list ofwinter B. napus lines that are expected to work well in connection withthe disclosed process would include Columbus, Jetton, Darmor, Campala,Casino, Bristol, Plainsman, Jet Neuf, Wichita, Major, Samourai, andCeres. Some of these winter lines are European B. napus lines whileothers are North American winter lines. As explained below, springmodified B. napus lines of the present disclosure may be useful increating hybrid spring B. napus lines. If such hybrid B. napus linesemploy a parent line derived primarily from North American sources,using European winter B. napus lines in the present method may provide arich source for diverse genetics that may further enhance heterosis.

In one embodiment, the winter B. napus line is a canola-quality line,i.e., it produces seed with oil having no more than 2% erucic acid andmeal that contains no more than 30 micromoles of the previouslyidentified glucosinolates per gram of meal. This can help quicklyproduce a canola-quality modified B. napus in accordance with theinvention. In another useful approach, however, the winter B. napus lineis not a canola line, e.g., because the glucosinolate level in its mealis too high. Many European varieties of B. napus do not meet thedefinition of canola. As explained below, using such varieties in thisfirst cross can improve heterosis in further hybrid breeding.

Suitable rapid-cycle B. rapa lines are available under the trade nameWisconsin Fast Plants and available from multiple sources, includingCarolina Biological Supply Company of Burlington, N.C., US (“Carolina”).The Fast Plant Standard seed from Carolina is expected to work well,though the other seed types offered by Carolina may be useful forspecific breeding goals.

In one implementation, this cross employs a female winter B. napus lineand a male rapid-cycle B. rapa line. The female line may exhibitcytoplasmic male sterility or may be emasculated manually. The pollenfrom the B. rapa line would then be available to pollinate the B. napusline. In other embodiments, the B. rapa may be the female line (e.g., bymanual emasculation) and the B. napus may be the male line.

As noted above, the present disclosure provides a method in which awinter B. napus line is crossed with a rapid-cycle B. rapa line toproduce at least one F1 plant that is a modified B. napus line. B. napusis commonly understood to be an allopolyploid with an “A” genometraceable to B. rapa and a “C” genome traceable to Brassica oleracea.Crossing B. napus and B. rapa in accordance with embodiments of thepresent invention, therefore, is believed to modify the A genome of thewinter B. napus line while leaving the C genome largely intact. Thoseskilled in the field may refer to the F1 plant as a B. napus or as a“modified” B. napus, with “modified” possibly being furthercharacterized as a “partially reconstituted” or “species interspecific”.For purposes of clarity, the term “modified B. napus” shall be deemed toencompass plants that result from a cross of a B. napus line and a B.rapa line, as well as progeny of such a cross. Furthermore, the term B.napus as used herein shall encompass both conventional and modified B.napus.

A surprisingly high percentage of the F1 plants that come from thedescribed B. napus×B. rapa cross are spring B. napus. It is worth notingthat the scope of a spring flowering habit encompasses a rapid-cycleflowering habit, as well. Spring F1 plants of the present inventioncould, but certainly need not, have a rapid-cycle flowering habit.

Many commercially desirable F1 plants will have a spring floweringhabit, but not a rapid-cycle flowering habit, i.e., will germinate,initiate vegetative growth, undergo gametogenesis and flower in 21-55days under SGCs. Although rapid flowering is a desirable characteristic,rapid-cycle B. rapa may have a rather short time from planting to fullmaturity. The Wisconsin Fast Plant Program indicates that the WisconsinFast Plants, for example, mature within about 40 days after planting.Shorter growing seasons for B. napus are typically associated withreduced yield and/or lower oil quality, so a very short time to maturitymay be expected to adversely impact yield and/or oil quality. Aspects ofthe present invention, however, yield spring B. napus lines that areexpected to have very good agronomic and oil quality characteristics.

The resultant F1 hybrid may or may not produce canola-quality seed. If anon-canola B. napus is used as the winter line in making the F1, thereis a good chance that some or all of the resultant F1 plants willproduce seed that fail to meet the canola definition stated above. Inone implementation, the F1 plants may be screened to identify seed thatboth has a spring flowering habit and produces canola-quality seed.

As noted above, Osborn and others have proposed crossing winter andspring B. napus lines and selecting spring B. napus plants from theresultant F1 population. Unfortunately, many of the plants in the F1population are not spring B. napus. Osborn suggests using geneticscreening of vfn1, vfn2, and/or vfn3 loci to identify plants that areexpected to have a spring growth habit (as that term is used in theOsborn patent). Such screening may be less expensive than growing all ofthe F1 population to see which plants will have a spring floweringhabit, but it adds complexity to a breeding program.

Aspects of the present invention provide a surprisingly high springconversion efficiency, where “spring conversion efficiency” is thepercentage of the F1 population resulting from the winter B.napus×rapid-cycle B. rapa cross that has a spring flowering habit. Incertain implementations, this spring conversion efficiency is at least80%, desirably 85% or more, and preferably at least 90%. As explained inconnection with the examples below, winter B. napus×rapid-cycle B. rapacrosses have yielded an astounding 100% spring conversion rate in thisfirst cross, i.e., all of the F1 plants have a spring flowering habit.

Backcrossing Spring B. napus with Winter B. napus

In accordance with a further embodiment, the F1 seeds produced by thewinter B. napus×rapid-cycle B. rapa cross outlined above (or progeny ofthe F1 seed) are crossed again with a second winter B. napus line toyield a first backcross plant (BC1). The F1 seed used in this secondcross desirably has a spring flowering habit. At least a significantpercentage, if not all or substantially all, of the BC1 plants may havea spring flowering habit.

In one embodiment, this second cross is a true backcross, i.e., the samewinter B. napus used in the first cross is used in the second cross withthe F1 seed. In other embodiments, the first winter B. napus line usedin the first cross is different from the second winter B. napus lineused in the second cross. This may not be considered a true “backcross”as that term is conventionally used, but the term backcross as usedherein in connection with producing the present BC1 plant (andsubsequent BCn plants) is intended to encompass a cross of a springmodified B. napus F1 (or BCn) plant as described above with any suitablewinter B. napus line. Even if there is no recurrent parent in the crosspollination, the term “backcross” is intended to reflect the cross aspring modified B. napus or its progeny “back” with any winter line.

The resultant BC1 seed may be subjected to any number of additional“backcrosses” with winter B. napus. Preferably, the BC1 seed used insuch an additional backcross has a spring flowering habit; if the BC1population includes some plants that do not have a spring floweringhabit, one can test the BC1 seed and select only those plants that havea spring flowering habit. In some embodiments, each of these backcrossesis a true backcross, i.e., the winter line is the same in the firstcross to produce the F1 seed and in each of the subsequent crosses. Inother embodiments, the winter line used in a subsequent cross may differfrom one or more of the winter line(s) used in the previous crosses. Forexample, the BC1 seed may be crossed with a third winter B. napus lineto produce a second backcross plant (BC2) and the third winter B. napusline may be different from one or both of the first and second B. napuslines used to produce the F1 and BC1 plants, respectively.

This process may be repeated to create a whole series of backcrossgenerations, BC1, BC2, BC3, . . . BCn. In each backcross, the winterparent may be a recurring parent from the preceding cross (a truebackcross). Alternatively, two or more different winter lines may beused in the backcrosses. In each such backcross, a backcross populationmay be created and plants having a spring flowering habit may beselected from that population.

Further Hybrid Breeding—Spring

In another further embodiment, seed produced by crossing the winter B.napus line and rapid-cycle B. rapa line as noted above can be crossed ina second hybrid cross with another spring B. napus to produced a secondhybrid B. napus, referred to herein as a F′1 hybrid, with a springflowering habit. In this embodiment, the F1, BC1, BC2, . . . BCn seeddescribed above, or progeny of such seed, may be used in the secondhybrid crossing step. If so desired, seed from a suitable F1 or BCnplant having a spring flowering habit may be selfed one or more times toincrease the amount of available seed. The selected seed (whether aselected F1 or BCn plant or the higher volume of seed from selfing) maybe crossed with an existing spring B. napus line to form F′1 plants andplants having a spring flowering habit may be selected from the F′1population.

Such an approach can be particularly advantageous in breeding acommercial canola line, for example. As noted above, the winter B. napusline selected for the initial cross to form the F1 hybrid may be anon-canola line. The genetic differences of such lines from mostcommercial spring canola lines will tend to be greater than suchdifferences from most winter canola lines. At least some of this geneticdifference is expected to be found in the F1 seed and in backcrosses andother progeny thereof. When the F1 seed is crossed with an existingspring B. napus line, the genetic differences between the two parentlines may enhance heterosis, producing F′1 plants that have better yieldand/or vigor.

In one specific embodiment, therefore, the F1 line (or its progeny)selected for the second hybrid cross is a non-canola line. Thisnon-canola F1 line is then crossed with a spring B. napus line thatmeets the canola definition and the resultant F′1 plants may be screenedto select those that are canola quality.

As explained above, crossing B. napus and B. rapa in accordance with thepresent invention is believed to modify the A genome of the winter B.napus line while leaving the winter line's C genome largely intact. Thismeans that a significant majority of the winter line's genetics will becarried forward into the modified B. napus F1 plants that result from B.napus×B. rapa cross.

In contrast, crossing spring×winter B. napus as proposed by Osbornresults in modification of both the A and C genomes. Osborn teachesselecting a F1 plant from such a cross that has a spring growth habitand crossing that F1 plant with another spring line. This furtherdilutes the winter germplasm in the spring-stable line. Creating aspring modified B. napus and “backcrossing” that F1 plant (or itsprogeny) with another winter line, however, reinforces the wintergenetics in the A genome while retaining a winter-derived C genome.

Methods in accordance with embodiments of the invention thus introducesignificant new germplasm from winter lines' C genome into a spring B.napus breeding program. This largely untapped pool of germplasm isexpected to increase heterosis in spring B. napus hybrids such as theF′1 plants noted above. As heterosis is associated with increased yield,this is expected to enable higher-yielding B. napus varieties.

Further Hybrid Breeding—Winter

Aspects of the invention can also be used to substantially speed up awinter B. napus breeding program. In accordance with one such method, aspring BC1 B. napus such as that described above is crossed with awinter line to form a backcross population. At least one secondbackcross plant that has a winter flowering habit is selected from thatbackcross population; this winter plant is referred to below as a BC-Wto note its winter flowering habit. As a result, the breeding programtakes a winter B. napus, creates a spring B. napus in which much of thewinter C genome is believed to be intact, and then converts that springB. napus back into a winter B. napus. Particularly if the first andsecond backcrosses are true backcrosses employing the same winter lineused in the first cross with the rapid cycle B. rapa, this can leavesome key genetics in the winter line intact through the complete cycle.

This embodiment process has particular commercial significance ifmultiple crosses are conducted using plants with a spring floweringhabit before selecting the BC-W line with the winter flowering habit. Asnoted above, a series of backcross generations—BC1, BC2, . . . BCn—maybe created. The spring conversion efficiency of these backcrossesremains fairly high even through multiple generations, so one cancontinue to select a plant from the backcross population that has aspring flowering habit.

Because most winter B. napus lines require vernalization, the time fromplanting to maturity for a winter B. napus is significantly longer thanthat for a spring B. napus. This means that spring breeding programs cantake advantage of more greenhouse cycles per year than a similar winterbreeding program, reducing the total time to develop a desired trait.

Employing the present embodiment, however, a winter breeder can achievemuch the same greenhouse cycle times as a spring breeding program byusing the BC1-BCn spring B. napus generations described above. As eachof these “backcrosses” permits the introduction of another winter B.napus line, the development time of the winter B. napus traits isgreatly reduced. Once the breeder has developed such a spring B. napuswith the desired traits, that spring B. napus can be crossed withanother winter B. napus to create a backcross population and a resultantplant having a winter flowering habit may be selected from thatpopulation. This new winter B. napus line can then be used in thebreeder's standard winter breeding program.

Because the rapid-cycle B. rapa appears to impact only the A genome inthe F1 generation and the C genome from the winter parent(s) appears tobe largely intact, a winter breeder can carry many of the traits ofinterest from his or her winter lines through multiple generations ofspring breeding. When the breeder selects a plant with a winterflowering habit (referred to as BC-W above) from a backcross population,therefore, there appears to be a good likelihood of successfullycarrying forward the developed trait from the spring backcrossgenerations into the BC-W plant and its progeny.

EXAMPLES

Aspects of certain methods in accordance with embodiments of theinvention are illustrated in the following examples.

Example 1 F1 Hybrid Cross

Seeds of three winter B. napus lines—Columbus, Jetton, and Darmor—wereplanted and stored in cold conditions for three months for vernalizationbefore being moved to a greenhouse. Fast Plant Standard seed fromCarolina, identified below as FPS, was found to flower in 18 days atSGCs so it was determined to have a rapid-cycle flowering habit. AnotherB. rapa line, AcBoreal, was found to flower at 27 days at SGCs, so ithas a spring flowering habit and is not a rapid-cycle B. rapa line.

Each of the three winter B. napus lines were crossed with each of the B.rapa lines to make 5 plants of each cross. The winter B. napus lineswere male sterile (they were emasculated or exhibited geneticcytoplasmic male sterility) and served as the female parent; the B. rapalines were used as the male parent. The resultant F1 populations of eachcross were grown under SGCs to determine their time to flowering. Thetime to the earliest flowering was noted for those plants that didflower; if no flowers were seen within 4 months at SGCs, the plant asnoted as non-flowering. The results are shown in Table 1.

TABLE 1 Female Male Flowering Parent Parent Plant Total Plants Days ofEarliest Flowering (winter B. napus) (B. rapa) ID Plants (%) Flower(SGCs) Habit Columbus FPS F1-C 5 5 (100%) ~30-35 Spring AcBoreal 5 0Non-flowering Winter Jetton FPS F1-J 5 5 (100%) ~35-40 Spring AcBoreal 50 Non-flowering Winter Darmor FPS F1-D 5 5 (100%) ~30-35 Spring AcBoreal5 0 Non-flowering Winter

The spring conversion efficiency results for these crosses areremarkable. Crossing the winter B. napus lines with AcBoreal, a B. rapawith a spring flowering habit, produced an F1 population in which everysingle plant had a winter flowering habit, demonstrating a springconversion efficiency of 0% (0 of 5 plants). Every F1 plant produced bycrossing the rapid-cycle B. rapa FPS line with the same winter B. napuslines had a spring flowering habit, showing a remarkable 100% springconversion efficiency (5 of 5 plants). This 100% spring conversionefficiency is impressive in its own right, but is made even moreremarkable in comparison to the cross with AcBoreal, which itself has aspring flowering habit but did not yield a single F1 plant with a springflowering habit.

Example 2 Backcross 1 (BC1)

Seed from one of the F1-C plants (Columbus×FPS cross) and one of theF1-J plants (Jetton×FPS cross) were then backcrossed to the originalparent line, i.e., the F1-C was backcrossed with Columbus and the F1-Jwas crossed with Jetton. Twenty plants of each cross were produced. Ineach instance the winter B. napus line was used as the male and the F1seed produced in Example 1 was used as the female. The resultantbackcrossed seed (BC1) was planted and grown at SGCs and the time to theearliest flowering was noted for those plants that did flower; if noflowers were seen within 4 months at SGCs, the plant as noted asnon-flowering. The results are shown in Table 2.

TABLE 2 Female Parent Male Plant Total Flowering Days of Earliest(Winter B. napus) Parent ID Plants Plants (%) Flower (SGCs) ColumbusF1-C BC1-C 20 8 (40%) ~30-43 Jetton F1-J BC1-J 20 1 (5%)  ~40

Example 3 Backcross 2 (BC2)

Seed from the plant with the shortest flowering time for each backcrossin Example 2 was then used as the male line in a cross with a femalewinter line. The Jetton backcross (BC1-J) was backcrossed to Jetton andthe Columbus backcross (BC1-C) was “backcrossed” with a variety ofdifferent winter lines, as noted in Table 3. Ten to twenty-five plantsof each cross were produced, also as noted in Table 3. The resultantbackcrossed seed (BC1) was grown at SGCs and the time to the earliestflowering was noted for those plants that did flower; if no flowers wereseen within 4 months at SGCs, the plant was noted as non-flowering.

TABLE 3 Days of Female Flowering Spring Plants Earliest Parent MaleTotal Plants (percentage of Flower (Winter B. napus) Parent Plant IDPlants (%) total plants) (SGCs) Columbus BC1-C BC2-C 20 15 (75%) 12(60%) 30 Jetton BC1-J BC2-J 25 20 (80%) 18 (72%) 31 Campala BC1-CF1(BC2)-A 20 18 (90%) 17 (85%) 32 Casino BC1-C F1(BC2)-B 20 18 (90%) 13(65%) 34 Bristol BC1-C F1(BC2)-C 20 19 (95%) 16 (80%) 33 Plainsman BC1-CF1(BC2)-D 10  9 (90%)  8 (80%) 32 Jet Neuf BC1-C F1(BC2)-E 20  20 (100%) 20 (100%) 28 Wichita BC1-C F1(BC2)-F 20  20 (100%)  20 (100%) 27

The results of this experiment show that the spring conversionefficiency remains quite high even though the male parent is already abackcross. All of the backcrosses had a spring conversion efficiency ofat least 60%, with the entire population resulting from two of thecrosses having a spring flowering habit. This suggests that asubstantial majority of the winter genetics can be retained in a BC2generation seed that has a spring flowering habit.

Example 4 Backcross 3 (BC3)

Seed that flowered in Example 2 was used as the male parent in a crosswith a winter line. In each case, a true backcross was made, e.g., BC2-Cwas crossed with Columbus. In addition, the earliest-flowering plant ofthe Wichita cross in Example 2 (designated F1(BC2)-F) was backcrossedwith different winter varieties, as noted below in Table 4. Twentyplants of each such cross were grown at SGCs and the time to theearliest flowering was noted for those plants that did flower; if noflowers were seen within 4 months at SGCs, the plant as noted asnon-flowering. For purposes of comparison, a known spring B. napus,Westar, was also planted under SGCs and the days to flower were noted.

TABLE 4 Female parent Male Total Days of Earliest (Winter B. napus)Parent Plant ID Plants Flower (SGCs) Columbus BC2-C BC3-C 20 46 JettonBC2-J BC3-J 20 50 Campala F1(BC2)-A BC1(BC3)-A 20 ~80 Casino F1(BC2)-BBC1(BC3)-B 20 56 Bristol F1(BC2)-C BC1(BC3)-C 20 47 Plainsman F1(BC2)-DBC1(BC3)-D 20 52 Jet Neuf F1(BC2)-E BC1(BC3)-E 20 52 Wichita F1(BC2)-FBC1(BC3)-F 20 37 Eric F1(BC2)-F F1(BC3)-G 20 48 Navajo F1(BC2)-FF1(BC3)-H 20 48 Contact F1(BC2)-F F1(BC3)-I 20 55 Mohican F1(BC2)-FF1(BC3)-J 20 46 Westar (spring) — —  5 37

Ten of the twelve backcrosses produced in accordance with an embodimentof the invention had a spring flowering habit. Of the two exceptions—theCampala backcross, BC1(BC3)-A, and the Casino backcross, BC1(BC3)-B—onehad a flowering time of 56 days and very nearly qualifies as having aspring flowering habit. This suggests that even after 3 backcrosses towinter B. napus, the progeny of the winter B. napus×rapid-cycle B. rapacross disclosed herein can yield B. napus with a spring flowering habit.

Although not shown in Table 4, the earliest-flowering plant of theWichita backcross, F1(BC2)-F, population was also crossed with Westarand another spring B. napus line. The resultant F1 hybrid had improvedvigor and appeared to have better yield, based on leaf size, larger podsize, and more seeds, when compared to either parent line.

Example 5 Comparison to Spring×Winter B. napus Crosses

A first spring×winter B. napus population was created by crossing aspring B. napus line with Columbus; as in Example 1, Columbus was malesterile and served as the female parent. The process used in Example 1to produce F1-C, i.e., crossing the FPS rapid-cycle B. rapa andColumbus, was repeated. Five plants of each cross were produced and theresultant seed was grown at SGCs for at least 100 days. The plant withthe earliest flowering time for the spring×Columbus cross (designatedhere as SW-F1) flowered in 43 days. The plant with the earliestflowering time for the FPS×Columbus cross (designated here as FPSC-F1)flowered in 31 days.

SW-F1 and FPSC-F1 were each backcrossed with Columbus. Thirty plants ofeach cross were produced and the resultant seed was grown at SGCs for atleast 100 days. The time to the earliest flowering was noted for thoseplants that did flower; if no flowers were seen in that time, the plantwas noted as non-flowering. The results, including for each cross theshortest first flowering time for any of the 30 plants and the averagefirst flowering time for those plants that did flower, are set forth inTable 5.

TABLE 5 Shortest Average Flowering Days of Earliest Days of No. FemaleMale Total Plants Flowering Earliest of Spring Parent Parent Plants (%)(Under SGCs) Flowering Plants Columbus SW-F1 30  3 (10%) 83 89 0Columbus FPSC-F1 30 18 (60%) 35 59 9

These results again highlight the surprising utility achieved bycrossing rapid-cycle B. rapa with winter B. napus in accordance withaspects of the invention. The SWC-F1 parent in the backcross of Table 5had a spring flowering habit that was reinforced through multiplegenerations of spring backcrosses and selection for spring floweringhabit. All thirty of the backcrosses of that plant with a winter linehad a winter flowering habit, i.e., the spring conversion efficiency ofthe cross was 0%, and the average number of days to earliest floweringof the three lines that did flower in the time allotted was almost 90days. In contrast, the FPSC-F1 backcross yielded 18 plants that floweredin the same time, with one reaching first flower in just 35 days. Ofthose 18 plants, 9 had a spring flowering habit, representing a 30%spring conversion efficiency (9 of the 30 total plants), with an averageamong those 9 plants of 47 days to earliest flowering.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense; that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number respectively. When the claims usethe word “or” in reference to a list of two or more items, that wordcovers all of the following interpretations of the word: any of theitems in the list, all of the items in the list, and any combination ofthe items in the list.

The above detailed descriptions of embodiments of the invention are notintended to be exhaustive or to limit the invention to the precise formdisclosed above. Although specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whilesteps are presented in a given order, alternative embodiments mayperform steps in a different order. The various embodiments describedherein can also be combined to provide further embodiments.

Unless otherwise indicated, all numbers expressing quantities ofingredients, properties such as molecular weight, percentages, reactionconditions, and so forth used in the specification and claims are to beunderstood as being modified by the term “about.” Accordingly, unlessindicated to the contrary, the numerical parameters set forth areapproximations that may depend upon the desired properties sought.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification, unless the above detailed description explicitlydefines such terms. Unless otherwise indicated, all numbers expressingquantities of ingredients, properties such as molecular weight,percentages, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified by the term “about.”Accordingly, unless indicated to the contrary, the numerical parametersset forth are approximations that may depend upon the desired propertiessought.

We claim:
 1. A method for producing a modified Brassica napus,comprising: crossing a first winter B. napus line with a rapid-cycle B.rapa line having a mean flowering time under standardized growingconditions of no greater than 20 days in a first cross, therebyproducing an F1 modified B. napus plant that has a spring floweringhabit; and thereafter, crossing seed from the F1 modified B. napus plantwith a second winter B. napus line in a second cross to produce a plantthat has a spring flowering habit.
 2. The method of claim 1 wherein thefirst and second winter B. napus lines are the same line.
 3. The methodof claim 1 wherein the first and second winter B. napus lines aredifferent lines.
 4. The method of claim 1 wherein the first cross has aspring conversion efficiency of at least about 80%.
 5. The method ofclaim 1 wherein the plant produced in the second cross is referred to asa BC1 plant, the method further comprising crossing the BC1 plant with athird winter B. napus line in a third cross to produce a plantpopulation and selecting from the population a second plant that has aspring flowering habit.
 6. The method of claim 1 wherein the plantproduced in the second cross is referred to as a BC1 plant, the methodfurther comprising crossing the BC1 plant with a third winter B. napusline in a third cross to produce a plant population and selecting fromthe population a second plant that has a winter flowering habit.
 7. Themethod of claim 5, wherein the third winter B. napus line is differentfrom at least one of the first and second winter B. napus lines.
 8. Themethod of claim 1 wherein the plant produced in the second cross isreferred to as a BC1 plant, the method further comprising crossing theBC1 plant with a spring B. napus line to produce a hybrid plant that hasa spring flowering habit.
 9. The method of claim 1 wherein the plantproduced in the second cross is referred to as a BC1 plant, the methodfurther comprising crossing the BC1 plant with a third winter B. napusline to produce a restored winter plant that has a winter floweringhabit.
 10. The method of claim 9 wherein the third winter line is thesame line as at least one of the first and second winter lines.
 11. Themethod of claim 9 wherein the third winter line is a different line fromboth of the first and second winter lines.
 12. The method of claim 9further comprising crossing the restored winter plant with a fourthwinter B. napus line.
 13. A B. napus plant having a spring floweringhabit, said plant being produced by the method of claim
 1. 14. Seed ofthe plant of claim 13 or progeny of said seed, said seed or progenyhaving a winter allele for at least one of vfn1, vfn2, and vfn3 loci butyielding a plant having a spring flowering habit.
 15. A method forproducing a modified Brassica napus having a winter flowering habit,comprising: crossing a first winter B. napus line with a rapid-cycle B.raga line having a mean flowering time under standardized growingconditions of no greater than 20 days in a first cross, therebyproducing an F1 modified B. napus plant that has a spring floweringhabit; thereafter, crossing the F1 modified B. napus plant with a secondwinter B. napus line in a second cross to produce a first backcrosspopulation and selecting from the first backcross population a firstbackcross (BC1) plant that has a spring flowering habit; and thereafter,crossing the BC1 plant with a third winter B. napus line in a thirdcross to produce a second backcross plant population and selecting fromthe second backcross population at least one second backcross (BC2-W)plant that has a winter flowering habit.
 16. The method of claim 15wherein the third winter line is the same line as at least one of thefirst and second winter lines.
 17. The method of claim 15 furthercomprising crossing the BC1 plant with a third winter B. napus line in afourth cross to produce a BC1 backcross progeny population and selectingfrom the BC1 backcross progeny population at least one BC1 progenybackcross plant that has a spring flowering habit.
 18. A B. napus planthaving a winter flowering habit, said plant being produced by the methodof claim
 15. 19. Seed of the plant of claim 18.